Internal combustion engines with modern electronic operation control units (engine management) have a sensor device which detects the rotational angle of the crankshaft. A crankshaft sensor and a camshaft sensor are usually employed for this purpose. Sensors have also already become well known by means of which the rotational direction of the crankshaft can be detected. Such sensor devices make it possible to determine the angular position of the crankshaft when the internal combustion engine is switched off.
When the internal combustion engine is started again, the angular position of the crankshaft is then immediately made available, which makes possible a correspondingly quick start of the internal combustion engine. This in its turn provides the option of designing the operation control unit in such a way that in order to save on fuel it automatically switches off the internal combustion engine when the vehicle comes to a standstill and starts it again as soon as a corresponding request from the driver is identified.
In the case of such a start of the internal combustion engine, the operation control unit may receive the information from the sensor device about a short reverse rotation of the crankshaft. This can for example be caused by an error in the sensor device; however it can also be an actual reverse rotation of the crankshaft, for example when on oscillating the crankshaft, the starter switches off too early.
On identifying a reverse rotation of the crankshaft, no system events such as for example, fuel injection or gas-mixture ignition should be initiated in order to prevent damage. If after a reverse rotation process, the sensor device again indicates a forward movement of the crankshaft, this may involve the forward phase of an oscillating process, but may also involve a continuation of the start process. Should it involve an oscillating process, no further action should be taken. If on the other hand, should the start process is continued, the initiation of system events such as fuel injection and gas-mixture ignition should be enabled again as soon as possible in order not to delay the start process further.
Therefore, the operation control unit should be in the position to determine whether or not the crankshaft of an internal combustion engine rotating forward after a reverse rotation is oscillating or is continuing its forward movement. This is a requirement for ensuring that a system event that has already occurred once such as for example a fuel injection in a specific cylinder is not repeated. Otherwise, too much fuel will arrive in this cylinder. In addition, the switching off of the injection and the ignition when the reverse rotation has taken place is exhaust-gas-relevant, because under the circumstances, cylinders contain a non-ignitable mixture or the mixture is discharged unburnt. For this reason, it would in addition be desirable in the event of reverse rotation having taken place to be able to diagnose a sensor device error.